Monolithic Electrode Supported Electro-Chemical Device Stack

Abstract

A design of and the process for forming a monolithic electrode supported electro-chemical device is provided. The electro-chemical device stack can be a solid oxide fuel cell stack. The monolithic stack comprises multiple planar cells connected in serial by planar ceramic interconnects. The cells have gas channels embedded in electrode layers in both anode and cathode sides. Thin ceramic electrolyte and interconnect are sandwiched between electrodes. The process comprises the steps of a). forming green cells by laminating green tapes of anode, electrolyte, and cathode, b). forming a green stack by laminating cells and interconnects, c). firing the green stack to form a stack scaffold, d). covering the stack exterior surfaces with a hermetic coating, and f). infiltrating catalysts into porous electrodes through gas channels to form an active stack.

1 . A monolithic electrode supported electro-chemical device stack comprising:
 a). a plurality of cells, each cell including, a bulk anode, a functional anode over the bulk anode, an electrolyte over the functional anode, a functional cathode over the electrolyte, and a bulk cathode over the functional cathode;   b). the anode, cathode, bulk anode, and bulk cathode comprise of porous scaffold and electro-chemically active catalyst particulate coating on the scaffold pore surfaces;   c). planer ceramic interconnects between the cells, bonded to bulk anode of a first cell and bulk cathode of a second cell;   d). cells and interconnects are substantially parallel to each other and form a planar stack of cells, stacked one on top of another bonded by interconnects;   e). a planar ceramic interconnect bonded to the top surface of the formed stack, and a planar ceramic interconnect bonded to the bottom surface of the formed stack;   f). an electronically insulating hermetic coating on the exterior surfaces of the stack, except for part of the top and bottom surfaces.   
     
     
         2 . The stack of  claim 1 , wherein the bulk anode and bulk cathode are porous, and have porosity between 20% and 50%. 
     
     
         3 . The stack of  claim 1 , wherein the bulk anode and bulk cathode have thicknesses between 0.5 mm and 5 mm, preferably of substantially similar thicknesses. 
     
     
         4 . The stack of  claim 1 , wherein the functional anode and functional cathode are porous, and have porosity between 10% and 30%. 
     
     
         5 . The stack of  claim 1 , wherein the functional anode and functional cathode have thicknesses between 10 μm and 100 μm, preferably of substantially similar thicknesses. 
     
     
         6 . The stack of  claim 1 , wherein the electrolyte is non-porous or without open porosity. 
     
     
         7 . The stack of  claim 1 , wherein the electrolyte has thickness between 5 μm and 50 μm. 
     
     
         8 . The stack of  claim 1 , wherein the anode scaffold, cathode scaffold, bulk anode scaffold, bulk cathode scaffold, and electrolyte are of the same material or materials having substantially similar sintering shrinkage and thermal expansion coefficients. 
     
     
         9 . The method of  claim 1 , wherein the anode scaffold, cathode scaffold, bulk anode scaffold, bulk cathode scaffold, and electrolyte materials are oxygen ion conductive metal oxides. 
     
     
         10 . The stack of  claim 1 , wherein interconnect is non-porous or without open porosity. 
     
     
         11 . The stack of  claim 1 , wherein the interconnect has thickness between 5 μm and 50 μm. 
     
     
         12 . The stack of  claim 1 , wherein interconnect material has sintering shrinkage and thermal expansion coefficient that is substantially similar as anode and cathode scaffold material. 
     
     
         13 . The stack of  claim 1 , wherein interconnect material is electronically conductive metal oxides, preferably Sr-titanate (Sr TiO3) with a n-dopant, including La x Sr 1-x NbyTiO 3  where x is between 0.01 and 0.5 and y is between 0.01 and 0.25. 
     
     
         14 . The stack of  claim 1 , wherein the hermetic coating has thickness of between 10 μm and 1 mm. 
     
     
         15 . The stack of  claim 1 , wherein the hermetic coating has a thermal expansion coefficient that is substantially the same as, or slightly smaller than, the CTE of electrode scaffold material. 
     
     
         16 . The stack of  claim 1 , wherein coating material is glass, glass ceramics, or electronically insulating ceramics. 
     
     
         17 . A monolithic electrode supported electro-chemical device stack of  claim 1  further comprises gas channels formed within bulk electrodes. 
     
     
         18 . The stack of  claim 17 , wherein gas channels are formed in either cross-flow or counter-flow arrangements. 
     
     
         19 . The stack of  claim 17 , wherein gas channels have circular, elliptical, rectangular or other cross-section shapes, and cross-section sizes not smaller than 0.2 mm and not greater than the thickness of the layers they are embedded in. 
     
     
         20 . A method for forming a monolithic electrode supported electro-chemical device stack comprising forming a stack scaffold:
 a). forming a first green cell scaffold, the first green cell scaffold having a green bulk anode scaffold, a green functional anode scaffold over the bulk anode scaffold, a green electrolyte over the functional anode scaffold, a green functional cathode scaffold over the electrolyte, and a green bulk cathode scaffold over the cathode scaffold;   b). forming a green ceramic interconnect over the first green cell scaffold;   c). forming a second green cell scaffold over the green interconnect, the second green cell scaffold having a green bulk anode scaffold, a green functional anode scaffold over the bulk anode scaffold, a green electrolyte over the functional anode scaffold, a green functional cathode scaffold over the electrolyte, and a green bulk cathode layer over the cathode scaffold;   d). repeat b) and c) for all other green cell scaffolds and green interconnects with the same process and structure to form a green stack scaffold;   e). free sintering the green stack scaffold into stack scaffold at temperature between 1200°-1700° C. in air for between 30 minutes and 5 hours;   f). coating the sintered stack scaffold exterior surfaces with green ceramic, glass, or glass ceramic;   g). firing the stack scaffold at temperature between 500° and 1000° to form hermetic surface coating.   
     
     
         21 . The method of  claim 20 , wherein forming the green cells comprises tape casting or screen printing of the green bulk electrode scaffold, green functional electrode scaffold, and green electrolyte, and green interconnect to form the green cells and stack prior to sintering. 
     
     
         22 . The method of  claim 20 , wherein the green bulk electrode scaffold and green functional electrode scaffold are formed with pore formers; the green electrolyte and interconnect are formed without pore former. 
     
     
         23 . The method of  claim 20 , wherein gas channels are formed in the green bulk electrode scaffolds. 
     
     
         24 . The method of  claim 20 , wherein the cells and interconnects are diffusion bonded after sintering. 
     
     
         25 . A method for forming a monolithic electrode supported electro-chemical device stack in  claim 20  further comprising:
 a). providing a stack scaffold having porous bulk electrode scaffolds, porous functional electrode scaffolds, dense electrolyte, dense interconnects, and embedded gas channels; 
 b). providing an anode catalyst precursor and a cathode catalyst precursor; 
 c). infiltrating the anode catalyst precursor through the gas channels embedded in bulk anode scaffold; 
 d). infiltrating the cathode catalyst precursor through the gas channels embedded in bulk cathode scaffold; 
 e). heating the stack to between 500° C. and 1000° C. for between 10 minutes to 5 hours to convert precursors to catalysts, and henceforth convert the stack scaffold to an active stack. 
 
     
     
         26 . The method of  claim 25 , wherein infiltrations are performed in a vacuum between 100-300 mbar. 
     
     
         27 . The method of  claim 25 , wherein operations c), d), and e) are repeated until specific amount of the anode catalyst and cathode catalyst are deposited into electrode scaffolds. 
     
     
         28 . The method of  claim 25 , wherein the anode and cathode catalyst precursors comprise metal nitrate solution in sociochemical compositions that are converted to anode and cathode catalysts after heat treatment, respectively.